One important consideration is I wanted to avoid chewing into the tree roots.

Two problems we've had with acrylic that were combined with the tub surround... tenant burning tea light candles on the soap dish burned a hole in the surround and another tenant couple (both overweight) who enjoy taking showers together caused the tub and surround to flex so it became detached from the wall.

I know you will probably be busy rooting for the GIANTS this weekend, but you could do worse than spending time reading these forums and gathering all the amazing information and knowledge!

Once the root of the problem is solved, spray the affected areas with a 50/50 solution of bleach and water, and then replace the dry wall with new material.

Forever we were forced to use cast iron and clay tile, even though cast iron was much more expensive and required a lot more labor to install and clay tile was much more expensive as well and much more susceptible to tree root damage.

(/steps down from soap box, we can get back to REI now)

We provide a starter set of amenities (laundry & dishwasher detergent, trash bags, paper products, bathroom soaps/toothpaste/sunscreen) type stuff. 

If you want, you could add a tree that once grown will provide shade, but that will require raking up the leaves in the fall and depending on the location and wind, cleaning out the gutters more often....and the roots may cause problems later on.

I know instead of worrying more than I should I will break down the problem into its root and go from there.

If the company comes out again, ask them how they installed it, what is the root cause of the issue, and where in the manual it says the maintenance they are suggesting you do.